1. Field of the Invention
This invention relates to method and apparatus for suppressing dust and frictional ignition in the operation of a mining machine and, more particularly, to a continuous mining machine having a cutter drum equipped with rotary water seals that permit water to be conveyed from a source into the center of the drum sections and along the lengths thereof externally of the drum sections to outlets positioned on cutter bits from which water is sprayed onto the mine face as the mine material is being dislodged to suppress the generation of dust and the occurrence of frictional ignition.
2. Description of the Prior Art
In underground mining operations using either longwall shearers or drum-type continuous miners, it is well known to locate water spray nozzles on the cutting drum near each bit to suppress the generation of airborne dust and frictional ignition as the cutter bits engage the mine face. It is also known to suppress airborne dust and wet dislodged material by mounting spray nozzles on a bar located behind the cutter drum. The bar mounted spray nozzles wet the mine material above and below the cutter drum and also wet the bits as the cutter drum completes each rotation.
The effectiveness of a spray bar is limited and does not effectively control dust before it becomes airborne. However, the incorporation of spray nozzles with the cutter bits on the surface of the cutter drum has been found to be effective in suppressing dust before it becomes airborne. The water is continuously sprayed from the bits at the point where the material is dislodged from the mine face. Generating a water spray at the bits suppresses the dust at its source and effectively eliminates any risk of frictional ignition as the cutter bits strike the solid material. Generating a water spray from the nozzles also serves to extend the life of cutter bits on for both longwall miners and continuous miners.
It is the conventional practice to supply water to the nozzles on the surface of a shearer drum and a continuous miner drum from a water supply on the miner. For example, water is supplied from the cooling circuits of the drive motors and conveyed through conduits in stationary struts and housings to a rotary seal mounted concentrically on the axis of the drum. The rotary seal has a stationary part with ports for receiving the water and a rotational part mounted on the drive shaft. The water is directed inwardly through the rotary seal to a channel extending on the axis of the drive shaft. The water is conveyed through the drive shaft to a manifold connected by fittings to the spray nozzles associated with the cutter bits. The spray is directed from behind the cutter bits onto the area where the bit strikes the mine face.
A critical aspect in supplying water through a cutter drum to the external surface behind the cutter bits is the effectiveness of the rotary seal to prevent leakage of water into the gearcase and bearings. This problem is more readily solved with a longwall drum shearer because the drive shaft is more accessible for water supply and a smaller diameter rotating seal can be used compared to what is required for a continuous miner. A relatively large rotating seal must be used around the drive shaft of a continuous miner. This problem is further complicated with continuous miners having multiple sections. A typical continuous miner includes a pair of end drum sections and an intermediate drum section. Each section has a separate drive shaft as opposed to a single drive shaft with a longwall drum shearer.
In addition to preventing contamination of the gearcase and bearings, the rotary seal must withstand periods of time in which it runs dry where water is not circulated to the seal. The seal must also be protected from damage due to the accumulation of dirt in the water passageways and plugging of the sprays by pipe scale. In addition, the rotary seal must accommodate water leakage at the point where water passes from the stationary component of the seal to the rotating component of the seal.
Preferably, the rotary seal is installed on the drum section as a sealed unit to permit the conversion of a conventional continuous miner to one that supplies water to nozzles associated with each cutter bit on the cutter drum. The seal must be mounted so that it can be accessed without disabling operation of the mining machine for an extended period of time. The seal must be readily accessible for repair and replacement when required.
A number of systems have been proposed for sealing the rotating and stationary components through which water flows in generating a spray behind the cutter bits of a continuous mining machine. For example, U.S. Pat. No. 3,698,769 discloses a mining machine having a boom supported cutter drum in which a liquid inlet extends through each boom arm from a pressurized source of water. A tube is connected to a nonrotatable connector which encircles a shaft that rotatably supports the cutter drums of the mining machine. The liquid supplied to the inlet flows through the tube and through an arrangement of bores in a stationary housing that surrounds the rotatable shaft. A housing is clamped to the drive shaft for rotation therewith and includes a number of chambers which are positioned oppositely of the bores that convey the water through the stationary housing. The water flows from the stationary housing into the rotatable housing where the water is conveyed to a bore that extends axially through the drive shaft. From the axial bore the water is conveyed to outlets that discharge the liquid from the periphery of the cutter drum. The fluid connection between the stationary housing and the rotatable housing is sealed by sealing rings which prevent leakage to the bearings and gears but allows leakage past the rings externally of the mining head so that it may be readily and quickly detected.
In U.S. Pat. No. 3,876,254 a mining machine is disclosed in which liquid is supplied for dust suppression on the cutter drum. The liquid is supplied from a source to a channel in the wall of a stationary gearcase. The channel extends through the gearcase to a fluid transfer apparatus at an interface between stationary and rotating members. The transfer apparatus includes rotary seals in which water enters a space between a stationary portion of the seal and a rotating portion of the seal. The water pressure maintains the sealing members in sealing relation with the surrounding housings and a loss of liquid pressure reduces the pressure against the sealing members. From the rotary seal the water is conveyed through channels to the surface of the cutter drum from which the water is emitted from spray nozzles positioned on the periphery of the cutter drum.
With the mining machine disclosed in U.S. Pat. No. 3,374,033 water is circulated into the cutter drum and is discharged from nozzles into the kerf where cutting of material from the mine face takes place. The cutter drum is rotated by a shaft within a nonrotatable sleeve. A sealing ring is positioned between the rotatable shaft and the nonrotatable sleeve. The sealing ring includes openings that register with ports for water to pass through passages from the sleeve to a cutter wheel where the passages terminate at nozzles located in advance of the bit holders on the surface of the cutter drum. A sealing ring is positioned between the rotatable shaft and nonrotatable sleeve and bears against a valve ring which includes an arcuate passageway that supplies water to the nozzles from the passages and the nonrotatable sleeve in a predetermined arc of travel of the cutter wheel. In this manner, water is discharged from the nozzles onto the cutting face in a preselected arc so that the water is discharged just when the cutting is taking place and where dust is being generated.
U.S. Pat. No. 4,565,410 discloses a nozzle positioned near the periphery of cutting elements on a longwall mining machine for discharging liquid onto the coal face during the cutting operation. Valves control the flow of liquid to the nozzles so that liquid is discharged therefrom when the nozzles are opposite the coal face immediately ahead of the shear drum during the cutting operation. The valves prevent the supply of high-pressure liquid to those nozzles of the drum which are not directed to the mine face.
U.S. Pat. No. 3,767,265 also discloses dust suppression equipment on a longwall mining machine in which a fixed tube extends along the axis of a hollow drive shaft for feeding dust suppression fluid from the body of the machine toward the shearer drum. Water is supplied through the tube to a distributor located within the drum and arranged to feed the water to a plurality of pipes located angularly around the drum. A phasing disc is mounted on the end of the tube to rotate only with the tube so that the water is conveyed to only selected passages associated momentarily with the cutting zone of the shearer drum.
U.S. Pat. Nos. 3,876,253; 4,660,892; and 4,852,947 further disclose mining machines with rotating cutter drums having sealed piping systems that deliver water through stationary housings to rotatable housings and through drive shafts to the surface of the cutting drums. U.S. Pat. Nos. 4,647,112 and 4,836,613 disclose mining machines having cutting elements provided with high pressure nozzles for generating a stream of water at pressures capable of dislodging material from the mine face.
With the above described devices conventional seal rings are used to provide a rotary seal between the stationary and rotating components of the cutter drum. Also as pointed out above, the problem of maintaining an effective seal at the rotary interface is more acute in a continuous miner because of the large diameter required for the rotary seal in comparison with a smaller diameter rotary seal encountered with a longwall shearer drum. The large diameter rotary seal used in a continuous miner must operate for an extended period of time in a dust filled atmosphere to prevent leakage of the spray fluid to the bearings and gears within the gearcase. The seals must be supported within the cutter drum in a manner that permits efficient access for repair and maintenance without extended downtime of the mining machine.
More recently rotary water seals for mining machines have been proposed for preventing leakage of water into the gearcase and operating dry for extended periods of time when water spraying is not utilized. When water seals run dry they harden and loose their sealing capabilities. The seals must then be replaced which is a difficult task when the machine is operating at the mine face. Frequently the mining machine must be moved to a maintenance area or taken out of the mine to replace worn water seals.
A cartridge seal manufactured and sold by Cannings Seals Ltd., a British company, has been publicly tested by the U.S. Bureau of Mines for use with water spray systems mounted on mining machines. The cartridge seal consists of a double-faced sealing arrangement contained as a cartridge unit with a stainless steel housing. The seal assembly is comprised of two seal rings having opposed faces in which the rotating face is fabricated of resin carbon and the stationary face is fabricated of tungsten carbide arranged concentrically. To prevent leakage during operation, each of the face rings is lapped to a flatness within one wavelength of helium light band. In addition, multiple springs provide initial face loading before the addition of hydraulic forces and dowels maintain positive drive to all components.
The cartridge configuration of the Cannings seal ensures that the rotating and stationary components remain in correct axial and radial relationships during transit and fitting. A dirt-exclusion labyrinth seal keeps the seal clean in operation as a cartridge assembly. The seal, as a cartridge assembly, is a self-contained unit easily mounted, maintained and removed from the machine.
In operation of the cartridge seal, water is introduced to an axial port through the outer diameter of the unit and is channeled between the two seal face pairings to a further port in the component that rotates with the drive shaft. Secondary low pressure lip seals prevent incidental leakage of water crossing the seal faces, directing leakage to atmosphere. The cartridge seal is positioned within the cutter drum housing outside the gear housing to ensure that any seal leakage does not contaminate the internal bearings and gears. This cartridge seal is also reported as being capable of running dry for extended periods of time without damage.
While cartridge seals have proved to be effective in controlling the flow of water to the cutter drum of a continuous mining machine for suppression of dust and frictional ignition, further improvement is needed in a rotary seal for preventing liquid leakage into the gearcase housing and directing leakage to the atmosphere. The rotary seal must be capable of installation and removal at the work sight with a minimum amount of interruption in the operation of the mining machine. The seal must be readily accessible to lubricate the seal components within the cutter drum assembly to preserve the life of the rotary seal, particularly when the seal is run dry. The rotary seal must be positioned in the cutter drum housing to provide efficient access for hose connections and permit its replacement without loss of gear housing lubricant.
Other examples of rotary seal arrangements used in controlling the flow of water to the periphery of a cutting drum of a mining machine are disclosed in U.S. Pat. Nos. 4,660,892; 4,696,518; 5,054,858; 5,098,166; and 5,114,213 and published British Patent Specification Nos. 1,111,319 and 2,205,880.
While it is known to provide a rotary seal between the stationary and rotating components of a cutter drum assembly of a mining machine to supply a dust and ignition suppressing fluid to nozzles on the cutter bits, the known devices do not satisfactorily prevent leakage into the gearcase and at the same time provide lubrication of the rotary seal. Therefore, there is need for a rotary seal that effectively controls fluid leakage and is lubricated to resist wear in a fluid system for a cutter drum assembly.